Retroreflective signs have achieved widespread use for safety and informational signs along roads because of the high nighttime visibility they provide. In order to enhance the daytime visibility of such signs, it has been suggested to make the signs fluorescent as well as retroreflective. U.S. Pat. No. 3,830,682 (Rowland) discloses cube-corner type retroreflective sheetings which incorporate fluorescent dyes, e.g., rhodamine and fluorescein dyes. The resultant signs provide fluorescent ambient appearance and bright, colored retroreflection.
A problem with fluorescent retroreflective sheetings is that upon, in some cases relatively moderate, exposure to solar radiation, such as is encountered in sunlit outdoor applications, the fluorescent properties of the sheetings degrade. Many fluorescent dyes tend to fade or become colorless. This loss in fluorescent performance causes the ambient color of the subject sheeting to fade as well as changing the retroreflective appearance of the sign, thereby impairing the effectiveness of the sign and reducing the potential safety benefits thereof. In some instances, such degradation can occur over as short a time as six months.
U.S. Pat. No. 3,830,682 (Rowland) discloses retroreflective articles comprising synthetic plastic resins and fluorescent dyes such as rhodamine and fluoroscein dyes.
Japan Kokai No. 2-16042, Application No. 63-165914 (Koshiji et al.) discloses fluorescent articles comprising a screen layer and a layer containing a fluorescent coloring agent wherein the screen layer permits a defined range of transmission of light. According to the reference, the screen layer must have a transmittance of more than 30 percent at 370 nanometers and less than 20 percent at 340 nanometers. The reference further teaches that the coloring agent may be any fluorescent coloring agent and that the binder or matrix of the colored layer is subject to no critical limitation.